"Our findings were vastly different to previous studies that used strains not commonly associated with human disease," Tim Barnett says. "We now know that Streptococcus can hide, survive, and grow in cells." Above: Group A Streptococcus (green) grows inside a cell. (Credit: University of Queensland)

The microbe responsible for Group A Streptococcus, one of the world’s most fatal infectious diseases, can bypass the immune system and multiply within infected cells.

The findings are significant, researchers say, because they contradict previous understanding of how the bacterium behaves.

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“We studied M1T1, one of the most prevalent strains affecting the developed world,” says Tim Barnett from the School of Chemistry and Molecular Biosciences at the University of Queensland.

“It had previously been thought that autophagy, which is part of the immune response, efficiently defended the interior of cells against Group A Streptococcus.”

New research published in the journal Cell Host & Microbe shows that in fact M1T1 produces an enzyme that breaks down the patient’s immune proteins that fight bacterial infection.

“Our findings were vastly different to previous studies that used strains not commonly associated with human disease,” Barnett says. “We now know that Streptococcus can hide, survive, and grow in cells.”

Barnett and colleagues at the Australian Infectious Diseases Research Centre are using this discovery to continue investigations in the field.

The research is also relevant to a number of types of Group A Streptococcus, including M12 strain found in a recent outbreak of scarlet fever in Hong Kong.